Interface bonding between pavement layers is a key factor affecting the performance of any pavement structure. Over the years, several studies have been performed to better understand bonding between pavement layers. The first phase of this study was a laboratory assessment, which analyzed different parameters to better characterize the interlayer bond in pavements. Phase 2 of the study was a field validation and evaluation. This thesis, based on the results of phase 2, focuses on optimizing in-situ tack coat application rate and field installation. The main objectives of phase 2 were to validate the lab-determined optimum residual application rate for tack coat materials on a milled hot-mix asphalt (HMA) surface and to evaluate field performance of tack coat materials. Several parameters were analyzed, including the cleaning method prior to tack coat application, the paving procedure, tack coat type, and existing pavement surface texture. Tack coat materials used were SS-1h, SS-1hp, and SS-1vh (non-track tack coat). For the cleaning methods, the conventional procedures, broom and vacuum, were used on most of the sections and were compared to air-blast cleaning.
Two paving procedures were studied: the conventional paving method using a distributor truck and a regular paver, and the spray paver, which applies tack coat and paves at the same time.
Twenty-six sections were constructed on Interstate 80 in Illinois, and 19 sections were built on Illinois Route 98. The Interstate 80 test sections were constructed on three existing pavement surfaces: milled HMA, milled Portland cement concrete (PCC), and fresh binder stone mastic asphalt (SMA).
Two tests were used to analyze interface bonding: the interface shear test and the torque bond test. The test section on Illinois Route 98 was constructed on a milled surface. All specimens were cored in the field and tested at the Illinois Center for Transportation (ICT) using the Interface Shear Test Device (ISTD).
The results showed similar bond strength for the two types of cleaning methods; however, air-blast cleaning required use of a lower optimum residual application rate in the field to achieve the same bond strength. The bond strength at the interface when tack coat was applied with a spray paver is similar to the bond strength achieved when a conventional paver was used. The optimum residual application rate for milled surfaces obtained from the laboratory was 0.06 gal/yd2 (0.27 L/m2). This rate was validated at both test sites. The optimum residual application rate obtained for fresh binder SMA was 0.02 gal/yd2 (0.09 L/m2). SS-1vh performed better than any other tack coat material studied, and SS-1hp performed better than SS-1h.
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Identification of the optimum tack coat application rate will help ensure cost-effective and efficient tack coat application and will enhance pavement performance. It will also help the industry to better optimize resources and improve pavement performance.